The present invention relates to a control method for a hand-operated power tool and a power tool.
A protective mechanism for a drill is known from U.S. Pat. No. 5,584,619, which is supposed to protect the user from excessive stress when a drill bit is blocked. As soon as a blockade is detected or anticipated, the drill deactivates. Cases may occur where the drill bit gets jammed on a sustained basis.
In accordance with the principles of the present invention, a control method protects the user and works against sustained jamming of a drill bit.
In the case of the inventive control method for a hand-operated power tool, a driving electric motor rotates in a direction of rotation opposite from the direction of rotation prior to a blockade for a duration when a blockade is detected. Immediately following the duration, the electric motor again rotates in the direction of rotation prior to the blockade.
The control method has surprisingly proven to be qualitatively different from a short-term interruption of the power train by a slip clutch in the case of a blockade and periodic interruption in the case of a blockade on a sustained basis. In this case, even though the user can subsequently attempt to loosen the tool also with the support of the electric motor, tests show a much lower success rate than with an active reversal of the direction of rotation. This is surprising in particular because during a blockade most of the time the drill bit is not just jammed in the forward direction but also in the reverse direction. It is presumed that the relaxing of the drill bit when reversing the direction of rotation could have a positive effect. The additional value outweighs the apparent disadvantage of a higher stress on the drill when rotating against the standard direction of rotation for which gearwheels and couplings are not designed or for which they can be designed only with additional expense.
The hand-operated rotary power tool, e.g., for a drill bit, has an electric motor for driving a rotary tool, a sensor device for detecting a blockade of the tool; a triggering device, which, in response to a blockade by the sensor device reverses a direction of rotation of the electric motor prior to the blockade for a duration and immediately following induces the electric motor to rotate again in the direction of rotation. Thus, the direction of rotation changes after a blockade for a brief time from a forward direction to a reverse direction and immediately following again to a forward direction. In the process, the motor is not shut off in the meantime, but alternates between braking and accelerating. Changing the direction of rotation may also be repeated multiple times.
One embodiment provides that the duration is 25 ms to 1000 ms.
One embodiment provides for a sensor device to detect a blockade of the drill bit based on a power consumption, e.g., the current consumption, of the electric motor.
One embodiment provides that a rotational acceleration during a blockade is detected and the duration is determined as a function of the detected rotational acceleration of the housing. The lower the rotational acceleration when the drill bit strikes, the more stably a user appears to be able to guide the machine despite the blockade. It is clear that it is advantageous to increase the duration when the user is well able to guide the machine, i.e., the rotational acceleration is low. Otherwise the duration must be reduced.
One embodiment provides that after a first case of a blockade, threshold values for detecting a case of a second blockade are reduced for a second duration. After a blockade has been detected for the first time, as a precaution an immediately following blockade can already be expected when the drill bit is rotating forward. The reaction time is advantageously reduced thereby. The second duration may be two to five times the previously indicated duration.
The following description explains the invention on the basis of exemplary embodiments and figures.